Attenuation, or insertion loss in decibels, is the metric by which all hearing protection is judged by consumers and labeled as required by United States Environmental Protection Agency law. The standard solution to provide such protection has been physically occluding the ear canal with either a compressible, oversized earplug, typically constructed of expandable foam, silicone, putty/resins, or fibers. Thus a bias in the metrics of hearing protection performance to date has always been attenuation; however, this is a very narrow viewpoint which completely ignores often-important interface issues for the users. For example, a user's situation awareness and ability to localize sound stimuli is compromised. Comfort is often gained at the expense of attenuation. The occlusion effect causes unnatural sounding feedback of the user's own voice, making it difficult to modulate the voice output resulting in objections to using the protector and increasing the difficulty of achieving effective in-canal voice pickup for radio communications.
To further elaborate, current technology designed to provide both hearing protection and communications is based on the principle of occluding the outer ear in order to shelter it from the ambient environment. Most common is an earplug of some type which is inserted in the open ear canal, expanding along the radial surfaces of the canal as necessary until a physical seal is established. Furthermore, hearing protection devices, also known as HPDs, are only valuable when properly selected and fit to the user, and worn properly, to counteract imminent acoustical hazards, which unfortunately is often too late. Earplugs, by their very nature, introduce their own set of problems. They are frequently uncomfortable to wear, with the user being very aware of their presence. Additionally, due to significant differences between individuals with respect to the size and shape of their ear canals, it is difficult to provide a single earplug device that fits all users comfortably and effectively. As a result, many currently available earplugs suffer from the following problems, among others:                Production of the occlusion effect        Impaired localization        Compromised speech understanding        Severely degrades the user's situation awareness        Often ineffective protection due to improper sizing and insertion        Uncomfortable and unnatural feeling        Harbor and introduce bacteria and promote fungal infection        Challenges in compliance, that is, convincing the user to wear a HPD they “might” need        User's speech is too loud or too low        User's lack of confidence in actual protection provided and impaired situation awareness        Occlusion effect provides its own unnatural 15 dB of amplification of the user's voice in the ear canal        Impaction of cerumen, that is, earwax        Not compatible and interoperable with a user's (e.g., a soldier's) current ensemble and communications equipment.        
Thus, there remains a need to develop improved earplug devices which avoid or minimize the above-mentioned issues. In particular, it would be highly desirable to provide automatic attenuation for the preservation of a user's hearing functionality during and after noise hazards, while simultaneously providing for external signal detection and localization, as well as radio-connected and selectively attenuated ambient pass-through speech communications.